(1) Field of the Invention
The present invention relates generally to DC and AC homopolar generators, motors, and engines, and more particularly to an improved homopolar motor-generator used in applications where the starting torque is very large, such as motor vehicle applications.
(2) Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
The original design of a homopolar motor-generator, with a stator that produces a magnetic field and a rotor through which current passes, was developed by Faraday (see FIG. 1). In such a motor, the current J goes through the conducting disk between contacts 1a and 1b and the resulting J×B force (where B is the strength of the magnetic field at the rotating disk) creates a torque causing the disk to rotate. The main problem with such homopolar devices is that they have a very small working voltage (about 2-3 V) and a very large working current, which makes it difficult to change generator (or motor) parameters such as torque.
One design to reduce the working current (or to increase the working voltage) was proposed by Mueller, in U.S. Pat. No. 3,586,894. The Mueller patent describes a homopolar multi-disk motor-generator (see FIG. 2). It proposes placing coaxial disks in the gap of the electromagnet, where the stator disks are fixed to the magnet assembly, and the rotor disks are fixed to the shaft. The stator and rotor disks are electrically in contact in such a way that the current passing through the disks is directed through all the rotor disks serially and in the same radial direction. The wires from the power supply are connected to the end rotor disks by the brush-type collector; the electrical contacts between the disks are provided by axially extending annular ribs on the disks. This way, the total torque at the shaft is the sum of the individual torques developed in each rotor disk; as a result, this machine would significantly reduce the working current (or, equivalently, increase the working voltage) of the homopolar motor-generator, compared with Faraday's original design as shown in FIG. 1.
However, the machine described in the Mueller patent has a significant problem: the electrical contacts between the disks constantly arc, leading to a significant temperature elevation and heat damage in the ribs even at moderate linear velocities between the stator and rotor disks. Using brush collectors at the outer edge of the rotor disk (see FIG. 2) can be a significant problem due to the large relative velocity between the disk and the brushes.